In modern vehicles, a plurality of driver assistance systems assist the driver with driving the vehicle. Systems that take over acceleration and braking, as well as steering of the vehicle, from the driver in various situations are increasingly being used in passenger cars. When control of the vehicle is entirely taken over from the driver, the term “highly automated driving” or “autonomous driving” is also used.
In highly automated driving, the driver can engage in activities other than controlling the vehicle while traveling. The driver therefore cannot monitor the movement and surroundings of the vehicle. The result is that in some circumstances the driver cannot be called upon in the event of a required braking operation. Stringent demands in terms of availability are therefore placed on the braking system of such a vehicle.
Patent document DE 102 33 196 discusses a braking system that encompasses a hydraulically actuatable brake cylinder for actuating a brake. The system furthermore encompasses a pressure control cylinder with which a pressure in wheel brakes can be established. The pressure control cylinder can be acted upon by way of an electronic adjusting apparatus. In the event of failure of the pressure control cylinder, an assistance force can no longer be made available on the part of an assistance system. Such a failure can be, for example, a failure of the engine, with the result that a pressure increase by way of an assistance force is no longer possible, but instead can be provided only by the driver using muscle power.